US2285606A - Treatment of hydrocarbon oils - Google Patents

Description

' June 9,` 1942. w. NF-slNGER Erm. 2,285,606

' TREATMENT oF HYDRocARBoN'oILs Eiled sept 12, 1959 Patented `lune 9, 1942 TREATMENT OF HYDROCARBON OILS Charles W. Nofsinger and Joseph W. Jewell, Summit, N. J., assignors to Gasoline Products Company, Inc., Jersey City, N. J., a corporation of Delaware Application September 12, 1939, Serial No. 294,436

3 Claims.

This invention relates to certain novel improvements in the treatment and cracking of hydrocarbon oils and has in view particularly certain novel improvements in cracking and coking processes.

A primary object of the invention is to provide a method of processing crude petroleum for the purpose of producing desired yields of various products, particularly gasoline or motor fuel, fuel oil (residuum fuel oil) and coke.

With such object in View, the invention contemplates a process wherein the crude oil is subjected to fractional distillation to obtain a residue and condensate fractions adapted for cracking, the straight-run residue converted to coke and volatilized constituents from the coking operation and the straight-run condensate fractions subjected to cracking for the production of gasoline or motor fuel.

In accordance With the invention the crude residuum from the crude distilling operation is employed as the oil to be subjected to coking to obtain the desired yield of coke While the cracked residues, produced in the cracking of the condensate stock from the crude distilling and coking operations, and which consist largely, and as a matter of fact usually predominantly, of polymer products of cracking, are utilized to produce the desired yield of fuel oil. It is highly advantageous to reserve the crude residuum or virgin stock for the coking operation instead of coking the cracked residue because the coking of the crude residue produces relatively less gas and less refractory condensates than are produced by the coking of the cracked residue. It is, moreover, advantageous to reserve the cracked residue for the production of liquid fuel since the cracked residue possesses a higher specific gravity for a given viscosity than a topped or reduced crude and a consequent higher calorific value. In practicing the invention, therefore, the coking operation is applied to the topped or reduced crude to convert it immediately to ultimate yields of volatilized products including gasoline as Well as intermediate constituents adapted for high cracking per pass conversion into gasoline, while the cracked residue obtained from the cracking of the intermediate constituents recovered from both the crude distilling and coking operations is used to meet the desired yield of fuel oil.

It is a special object of the invention to provide a cracking process which, While taking advantage of the idea of cracking selected stocks in separate cracking zones in a practical Way,

will at the same time require a minimum amount of equipment. In accordance with the invention the crude oil may be subjected to fractional distillation in a separate distilling zone and the residue converted to coke in a separate coking zone and the volatilized fractions obtained in the crude distilling and coking operations may be refractionated in a common fractionating zone in which the vapors from the cracking Zones are subjected to fractionation for the recovery of the desired gasoline or motor fuel distillate as Well as for the separation into condensate stocks which are subjected to cracking.

One aspect of the invention is concerned with the recovery from a pressure cracking operation of a desired distillate of suitable boiling range and vapor tension from which distillate undesirable 10W boiling constituents will be excluded While retaining the constituents of desired boiling point and avoiding loss of such desired constituents in the exit gases from the system. In the furtherance of this object the invention contemplates the cracking of hydrocarbon oil under superatmospheric pressure with the fractionation of the cracked vapors and the collection of the desired distillate While still under superatmospheric pressure, With the flashing under reduced pressure of constituents derived from the cracking operation and the. stripping or fractionation of flashed constituents to obtain a fraction which shall be free from undesirable low boiling constituents and adapted as an absorb-v ent medium for recovering heavier constituents contained in the exit gases from the system which are desirable to retain in the distillate product. In one method of achieving this desired object the cracking is carried on under superatmospheric pressure and the cracked products are separated into vapors and residue and the vapors fractionated to recover the-desired distillate While still under superatmospheric pressure, the cracked residue is flash-distilled under reduced pressure and the flashed vapors are fractionated to vobtain a fraction Which shall be free from undesirable low boiling constituents and Which shall be Well adapted to serve the function of an absorbing medium to recover heavier constituents contained in the exit gases, such flashed fraction is brought into contact with the gaseous constituents which are separated from the distillate under superatmospheric pressure to absorb higher boiling constituents contained in the gases and the absorbent medium containing absorbed constituents is directed to the superatmospheric pressure fractionating zone so as to thereby effect retention of such constituents in the distillate product.

For the purpose of more fully disclosing the invention, reference is now had to the accompanying drawing which is a diagrammatic elevation of apparatus suitable for practicing a particular embodiment of the invention.

In the apparatus illustrated crude charging stock, after such preheating with hot products of the system as may be desired, is charged by pump I6 to a heating coil I I positioned in a furnace I2 by which the oil is heated to a desired distilling temperature and the heated' oil is passed into a stripping or fractionating tower I3 in which vapors separate from residue. The tower is provided with conventional fractionating elements and with suitable cooling and refluxing means to eiect the desired fractionation of the separated vapors, and provision may be made for introducing steam into the tower to aid the stripping of the residue formed therein. I'he vapors are fractionated to form a plurality of condensates which may be collected in trays such as I4, I5 and I6. The uncondensed vapors pass from the tower to a condenser coil I1 and the resulting distillate is collected in a distillate receiver or gas separator I8 provided with gas discharge line I9. The liquid collecting in the receiver I8 is directed by pump 20 to a rerun tower 2| reboiling the distillate and with conventional fractionating elements as well as cooling and reluxing means to accomplish the desired fractionation. The uncondensed vapors pass to a condenser coil 22 which discharge into a distillate receiver or gas separator 23r provided with a gas line 24 and a distillate line 25.

Residue from the crude stripping tower I3 is directed by a pump 26 to a heating coil 21 positioned in a furnace 28 adapted to heat the residue sufciently for coking and the heated residue is discharged into a coking chamber 29 in which the resi-due is retained for coki'ng'. In practice a plurality of coking drums are employed so that when the coking operation is completed in one chamber the discharge of oil from the heating coil 21Y may be diverted to another coking chamber while the former chamber may be cooled down and the coke removed. In this way the continuity of the complete rupted. The vapors from the coking drum pass to a fractionating tower 36' which may be equipped with conventional fractionating elements and with suitable cooling and refluxing means to accomplish the desired fractionation.

In the apparatus illustrated provision is made for drawing a heavy condensate from the bottom of the tower through a line 3l and for withdrawing an intermediate condensate by means of a tray 32 and a line 33. The uncondensed vapors pass to a condenser coil 34 discharging into a distillate receiver or gas separator 35 provided with a distillate line 36 and a gas line 31.

A heating coil 38 positionedin furnace 39 is provided for the cracking or reforming of light distillate. A naphtha fraction is withdrawn by pump 46 'from the fractionating tower 2l and conducted through charging line 4I to the heating coil 38 wherein it is subjected to temperatures adequate to effect cracking or reforming. The heated products are delivered by transfer line 42 to an evaporator 43. A heating coil 44 positioned in furnace is provided for crack'- ng an intermediate stock, su'ch as light gas oil or kerosene, and a heating coil 45 positioned in equipped with suitable heating means for process is not interfractionated therein.

a furnace 41 is provided for cracking a heavier fraction such as heavy gas oil. The heated products from coil 44 are delivered by transfer line 48 to the evaporator 43 and the heated products from the coil 46 are delivered by transfer line 49 to the evaporator 43. A tray 56 may be provided onto which the products from the heating coils 38, 44 and 45 may be discharged for the purpose of facilitating the vaporizing or evaporating of the hot cracked products, the liquid constituents overflowing to the bottom of the tower 43 while the separated vapors rise upwardly therein. The tower is equipped' with conventional fractionating elements and suitable cooling and reuxing meansl to1 accomplish the desired fractionation. A tray 5I is provided for collecting a primary or heavy condensate such as heavy gas oil and a tray 52 is provided for collecting a secondary or intermediate condensate such as light gas oil or kerosene. A pump 53 has an intake line 54 cornmunicating with lines 36, 33 and 3l so that any or all of the condensates from these lines may be introduced through a line 55 to the tower 43 to serve as arefluxing medium therein and so that the coke still distillate may be redistilled or re- Normally the coke still distillate introduced to the tower 43 will comprise light gas oil and heavy gas oil constituents and it is advantageous to introduce this distillate intermediate the trays 52 and 5I so that the heavy gas oil constituents may be combined with heavy reflux condensate forming in the tower and collecting in tray-5I while lighter gas oil constituents will pass upwardly as vapors and will be condensed, together with other vapors in the tower, and collected as a condensate in tray 52, while any lighter constituents present in the coke still distillate may pass overhead from the tower. The intake line 54 has a branch line 56 for withdrawing straight-run reflux condensate from tower I3, as from tray I4 of tower I3, so that the straight-run condensate may be combined with the coke. still condensate and refractionated in the. tower 43. A pump 51 serves to draw reflux condensate from tray 52 of tower 43 and direct. it to cracking coil 44 while a pump 5B conducts straight-run condensate from tray I5 of Y tower I3 through a une 59. to the cracking con 44. Primary or heavy vreflux condensate is drawn from tray 5I of tower 43 through a line 66 and directed by pump 6I through the cracking coil 46 and thence to the tower 43.

Uncondensed vapors from tower 43 pass to a subsequent fractionating. tower 62, preferably being introduced at an intermediate point thereof, for further fractionation therein. The tower 62 may be provided with heating means. at the bottom of the tower and with conventional fractionating elements and such cooling and refluxing means as may be desirable for accomplishing the required fractionation. Resulting condensate is withdrawn from tower 62 through a line 63 while uncondensed vapors pass to a condenser 64 which discharges into a distillate receiver or gas separator` 65. Distillate from theA receiver 65 is conducted by pump. 66 to a stabilizer 61 which is provided with suitable reboiling means, conventional fractionating elementsy and such cooling and refluxi'ng means as may be necessary to accomplish the. desired rectification of the distillate. Gaseous constituents from the stabilizer are removed through a Aline 68 while the stabilized-li-quid product is. withdrawn through a line 69.

Residue from the tower 43 is withdrawn through a line 1I and pressure reducing valve 12 to a flash drum 13 wherein vthe residue is flashdistilled under reduced .pressure and the distilled residue which constitutes a desired fuel oil product of the process is withdrawn through a line 14. The tower is equipped with conventional fractionating elements and with such cooling and refluxing means as may be necessary to effect the desired fractionation of the separated Vapors. A heavy or primary condensate collects in a tray 15 while a lighter or intermediate condensate collects in a tray 15. Uncondensed vapors pass to a condenser 11 `-discharging into a distillate receiver or gas separator 18. Primary or heavy reux condensate from tray 15 isdirected by a pump 19 through a line 89 which conveniently connects with ,line 55 for introducing the ashed condensate into the tower V43. Intermediate condensate Yfrom tray 16 of tower 13 is withdrawn through a line 8| thence to a heat exchanger 82 in which the condensate is subjected to cooling, thence through a subsequent cooler 83 to a receiving drum v84, having an outlet line 85. The cut collected .in drum 84 being the result of the flash-distillation, as well as the fractionation, in the low pressure tower 13, will be substantially free from lighter constituents, e. g., hydrocarbons boiling up to about 300 F. and is especially adapted for the absorbing operation which will now be described. This fraction collected in drum 84 is also well adapted as a furnace oil and any portions not required for the absorbing operation may be removed as a furnace oil product.

The gaseous constituents which separate from the liquid distillate under pressure in thereceiver -65 are passed through a line 86 to an absorber tower 81. This tower may be provided with a plurality of baies 88 as well as a section of contact material 89 in the upper portion of the tower. Distillate from receiver 84 is conducted by pump 99 through a line 9| to the tower 81 and the distillate is caused to ow downwardly over the baffles 88 in counter-current to the upwardly rising gaseous constituents so as to thereby absorb heavier components contained in the gaseous constituents. The unabsorbed gases are removed through a line 92. The liquid containing absorbed constituents from the gases is withdrawn by pump 93 and directed through a line 94 to an exchange element 95 in heat exchange with the distillate flowing through element 82 and is passed thence through a lin-e 96 to the tower 43, being preferably introduced at a point above the tray 52. Redistillation and refractionation of the distillate containing the absorbed hydrocarbons takes place in the tower 43 as well as in the subsequent fractionator 62 so that absorbed hydrocarbons may thus be combined with the distillate product which is collected in drum 55 and rectified in the tower 61. A pump 91 serves to draw distillate from receiver 18 and conduct it through a line 98 to the line 94 so that this distillate may be combined with the absorbent liquid and employed as a heat exchange medium in element 95 and directed to the tower 43. All of the distillate co1- lecting in tank 18, except such portion as may conveniently be used as a top reflux on the tower 13, may with advantage be returned to the tower 43.

A compressor 99 is provided with an intake line having a branch line |0I communicating with the gas line 31 of receiving drum 35 and a branch line |02 communicating with the gas line .I9 of receiving drum I8 so that gases from the crude distilling and coking operations may be directed through a line 03 to the pressure accumulator 6.5.' 'Certain heavier components which may be contained in the gases removed from the crude distilling and' coking operation, such as pentane, may thus be combined with the distillate collecting in the receiver 65' under the compression therein, whileuncondensed constituents are combined with the other gases being removed from Athe receiving drum and being pass-ed to the absorbing tower 81. The'light straight-run distillate collecting in receiving drum 23 may also be introduced into the receiver 65 and for'this purpose the pump |04 is provided having an intake line |05 for drawing distillate from drum 23V and a discharge line |06 communicating with line |03.

In a typical operation in accordance with the invention al crude petroleum is heated in the heating lcoil to ,temperatures of about 680 F. to 750 F. and delivered to the evaporator I3 wherein distillation takes place at approximately atmospheric pressure, forv example at 5 to 15 pounds gauge pressure. A temperature of about 680 F. to 725 F. is maintained in the bottom of the evaporatorv and the hot residue is passed directly to heating coil 21 wherein it is heated to temperatures of the order of 870 F, to 950 F. and passed to the coking drum for coking, preferably under pressures approximating atmospheric pressure and ordinarily not in excess of about 25 pounds. Reflux condensate at temperatures of 640 F. to 660 F.V is collected in tray l |4,r reflux condensate at temperatures of 500 F. to 585 F. is collected in tray |5 and reflux condensate at temperatures of 370 F. to 455 F. is collected in tray I6. It is advantageous to refra'ctionate all of these condensates in a side stripping tower (not shown), the refractionated condensate from tray I5 constituting kerosene, the refractionated condensate from tray |5 constituting a furnace oil or a light gas oil as may be desired and the refractionated condensate from tray I4 constituting a gas oil stock. Overhead distillate from tower I3 is collected in receiver I8 and refractionated in tower 2| to form a light gasoline or naphtha distillate collected in drum 23 and a heavy naphtha fraction suitable for reforming collected at the bottom of tower 2|.

The straight-run naphtha fraction from Vtower 2| is subjected to :reforming in heating coil 38, preferably under pressures of 700 or 750 pounds and at temperatures of 950 F. to 1000 F. Heavier straight-run gas oil stock from tray |4 is refractionated in the tower 43 together With distillate from the coking operation. The tower 43 'which receives the streams of hot products from the reforming coil 38 and cracking coils 44 and 45, is held under a pressure preferably in excess of or 200 pounds and usually at a pressure of about 250 to 260 pounds. A temperature of about '180 F. to 820 F. is maintained in the bottom of tower 43 while condensate is collected in tray 5| at a temperature approximating '790 F. and condensate is collected in tray52 at a temperature approximating 620 F. to 700 F. The condensate from tray 52 is cycled tothe `cracking coil 44 while lthe heavier condensate from tray 5| is directed to the heating coil 46 wherein it is subjected to cracking under pressureof about 400 to 600 pounds at temperatures around 925 F.

Overhead vapors from tower 4 3 pass to the tower atatemperature l@if @10.01411425 Eto 450 F. The tower 82 is maintained under approximately the same pressure as that of tower 43 and reboiling or reheating means are employed in the tower 62 to maintain a bottom temperature of about 515 F. to 550 F. Vapors pass from the tower at a. temperature of about 355 F. to 380 F. to condenser 64. The distillate is collected in receiving drum 65 under about 230 to 250 pounds pressure and at normal temperatures, for example 90 F. Straight-run gasoline distillate from receiver 23 is combined with the cracked distillate collecting in receiving `drum 65 and gaseous constituents from accumulators I8 and 35 are also directed to the receiving drum 65.

Residue from evaporator 43 is flash-distilled in ash tower 13 by means of its contained heat and preferably with the aid of steam. The pressure is materially reduced in tower 13 to approximately atmospheric pressure or to say 15 pounds gauge pressure. The temperature in the bottom of tower 13 is about 605 F. to '110 F. Condensate collects in tray 15 at a temperature of 580 F. to 640 F. and is directed to tower 43. Condensate collects in tray 18 at temperatures of 425 F. to 540 F. and is passed through heat exchanger 82 and cooler 83 for collection in receiver 84 at temperatures ordinarily not in excess of about 110 F. and usually at temperatures of about 65 F. to 10 F. It is recommended that the product collecting in receiver 84 shall have an initial boiling point of about 340 F. to 360 F. and an endpoint of the order of 580 F. to 620 F. The overhead distillate from tower 13 which collects in receiver 18 is refluxed in the tower 43. The overhead gaseous constituents from the gas separator 65, which constituents advantageously include the gases from the cracking operations as well as from the crude running and coking operations, are passed to the absorber tower 81 in which the pressure may be approximately the same as that in the receiver 65. Under the pressure-temperature conditions in the receiver 65, substantially all of the normally liquid hydrocarbons will be collected as a liquid therein, but this liquid will contain very material quantities of normally gaseous hydrocarbons, especially C4 hydrocarbons, butane and butylene and C3 hydrocarbons, propane and propylene. The gaseous fraction which passes to the absorber will contain normally gaseous constituents, hydrogen, methane, C2, Ca and C4 hydrocarbons and certain proportions of normally liquid hydrocarbons, more particularly C hydrocarbons or pentane. The special cut of absorbent oil produced in the flashing operation and collected in receiver 84 and having an initial boil-` ing point of about 340 F. is introduced into the absorber tower. At temperatures approximating normal or at temperatures of about 100 F., substantially all of the pentane and portions of the Cs and C4 hydrocarbons may be absorbed in the menstruum while the unabsorbed gases including hydrogen, methane and C2, C3 and C4 hydrocarbons pass out from the absorber. The menstruum containing absorbed C5 hydrocarbons is directed to the tower 43 for distillation and fractionation therein so that the absorbed C5 hydrocarbons enter into the distillate which is passed to the stabilizer 61. This distillate is rectified in the stabilizer 61 under pressures approximating 350 pounds with a bottom temperature of about 425 F. and a top temperature of 120 F. to 150 F. to produce a stabilized gasoline product and an overhead normally gaseous fraction containing predominantly C3 and C4 hydrocarbons. This gaseous fraction may be passed through a cooler wherein it is cooled to temperatures of about 65 F. to F. and collected under pressures of 100 to 225 pounds to constitute a product marketable as a bottled gas. The normally gaseous fraction from the stabilizer may also be used as charging stock to a polymerizing operation for conversion to normally liquid products.

Although a preferred embodiment of the invention has been described herein, it will be understood that various changes and modifications maybe made therein, while securing to a greater or less vextent some or all of the benefits of the invention, without departing from the spirit and scope thereof.

We claim:

1. In the cracking of hydrocarbon oils the process that comprises fractionating cracked vapors and gases formed as hereinafter specified to obtain fractions comprising a normally gaseous fraction including portions of normally liquid hydrocarbons, a gasoline fraction, a light gas oil fraction and a heavy gas oil fraction, recycling said light gas oil and heavy gas oil fractions to separate cracking zones wherein the oil is subjected to cracking conditions of temperature and pressure to effect conversion, directing the resultant cracked products from both of said cracking zones into a separating zone maintained under superatmospheric pressure wherein separation of vapors from liquid residue takes place, passing the separated vapors to the aforesaid fractionating zone, fractionally distilling crude petroleum in a separate distillation zone to separate light and heavy gas oil constituents from residue, directing such light and heavy gas oil constituents to the respective light gas oil and heavy gas oil cracking zones, passing residue from the crude distillation zone to a coking zone wherein it vis converted to form a coke residue, separately fractionating the vapors from the cokingzone'to form a condensate, flash distilling the residue from the aforesaid separating zone under reduced pressure and fractionating the flashed vapors to form a light fraction, an intermediate condensate and a heavier condensate, directing said heavier flashed condensate and said condensate obtained in fractionating the vapors from the coking operation to said frac-A tionating zone, directing the aforesaid gaseous fraction to an absorber zone and introducing the aforesaid flashed intermediate condensate to the absorber zone as an absorbing menstruum therein, passing said absorbing menstruum containing absorbed constituents from the absorber zone to the aforesaid fractionating zone` and rectifying said gasoline distillate to produce a product of desired boiling point and vapor pressure.

2. In the cracking of hydrocarbon oils the process that comprises fractionating cracked vapors and gases formed as hereinafter specified to obtain fractions comprising a normally gaseous fraction, a gasoline fraction, and a gas oil fraction, recycling said gas oil fraction to a cracking zone wherein the oil is subjected to cracking vconditions of temperature and pressure to eifect conversion, directing the resultant cracked products from said cracking zone to a separating zone maintained under superatmospheric pressure wherein separation of vapors from liquid residue takes place, passing the separated vapors to the aforesaid fractionating zone, fractionally distilling crude petroleum in a separate distillation zone to separate gas oil constituents from residue, directing such gas oil constituents to said cracking zone, passing residue from the crude distillation zone to a coking zone wherein it is converted to form a coke residue, separately fractionating the vapors from the coking zone to form a condensate, flash distilling the residue from the aforesaid separating zone under reduced pressure and fractionating the flashed vapors to form a light fraction, an intermediate condensate and a heavier condensate, directing said heavier ashed condensate and said condensate obtained in fractionating the vapors from the coking operation to said fractionating zone, directing the aforesaid gaseous fraction to an absorber zone and introducing the aforesaid flashed intermediate condensate to the absorber zone as an absorbing menstruum therein, passing said absorbing menstruum containing absorbed constituents from the absorber zone to the aforesaid fractionating Zone and rectifying said gasoline distillate to produce a product of desired boiling point and vapor pressure.

3. In the cracking of hydrocarbon oils the process that comprises fractionating cracked vapors and gases formed as hereinafter specied to obtain fractions comprising a normally gaseous fraction, a gasoline fraction, and a gas oil fraction, recycling said gas oil fraction to a cracking zone wherein the oil is subjected to cracking conditions of temperature and pressure to effect conversion, directing the resultant cracked products from said cracking zone to a separating zone maintained under superatmospheric pressure wherein separation of vapors from liquid residue takes place, passing the separated vapors to the aforesaid fractionating zone, fractionally distilling crude petroleum in a separate distillation zone to separate a condensate from residue, subjecting said condensate to cracking conditions of temperature and pressure to effect conversion, separating the resultant cracked products into vaporsA and residue, passing the separated vapors to the aforesaid fractionating zone, passing residue from the crude distillation zone to a coking Zone wherein it is converted to form a coke residue, separately fractionating the vapors from the coking zone to form a condensate, flash distilling the residue from the aforesaid separating zone under reduced pressure and fractionating the flashed Vapors to form a light fraction, an intermediate condensate and a heavier condensate, directing said heavier ilashed condensate and said condensate obtained in fractionating the vapors from the coking operation to said fractionating zone, directing the aforesaid gaseous fraction to an absorber Zone and introducing the aforesaid flashed intermediate condensate to the absorber Zone as an absorbing menstruum therein, passing said absorbing menstruum containing absorbed constituents from the absorber zone to the aforesaid fractionating zone and rectifying said gasoline distillate to produce a product of desired boiling point and vapor pressure.

C. W. NOFSINGER. JOSEPH W. JEWELL.

Images